The patron saint of Serbia, son of King Stephen I Nemanya, replaced his given name Rastko with Sava when he entered a monastery at Mount Athos. Personally I like Rastko better, but he's the saint so I guess he knows best. His father abdicated and followed him into the monastery, but Sava was summoned to return to Serbia when a quarrel for succession between his brothers threatened the peace and safety of their homeland. He crowned Stephen II (rather than the very badass-sounding Vulkan) and began work reforming the Serbian Church. He and his monastic brethren founded several monasteries, reformed the rules for the clergy, and sided with the Orthodox Church rather than the Church of Rome. In spite of this, he makes the Roman Catholic Canon of Saints as a peacemaker and an evangelist.
He published the first constitution of Serbia, and is rightly considered one of the founding national (as well as religious) figures. Bez muke nema nauke.